Looks exactly like the twin transistor amp we wrote about earlier but with a driver and 4 transistors in the final section. I remember testing it and putting it down cos I thought it got to hot. The fan inside does run most of the time when the power is on but it doesn’t do a good enough job. I think I was seeing close to 400W pep out of this with 20w of drive but will put it back in line and redo the results. These are mosfets. Great devices..it sounded oK and quite linear but it got hot and backed off….Somehow or other the makers have either got to run these at a fraction of their rated output or spread them out better on the board so they can run cooler. At the very least a fan on top!!!!
I am thinking that maybe some kind of computer type chip heatsinks and fans internally and some big fins and fans on top for starters and then spread the devices out as much as possible as well. This would work great if you could keep it cool…or else just run it at 250w or so….but it is good for a lot more….and it don’t cost but bugger all as well!!!
I will rerun the tests when I get time…..
TEST Time…May 21 2012
I contacted Eric in Magnum to enquire about getting a few more of these amps but was told they need a run of 200 before they will go into production. I don’t really think I would like to front up for 200 of them so for now you may have to look at similar models which I think are out in the marketplace somewhere.
Despite that I had the 74A switch mode PSU on the bench so wired it up to give it a run. Supply voltage was 14.2. I placed the power control on six because I don’t see the point in wasting power to heat up padding resistors. Better to turn the radio down. I was using a magnum S-45HP and turned the power down to around 30W pep. An easy 400W on the PEP meter. Probably the cheapest 400w out there when/if they start making them. Tested a DX500 as well and it pushed easily to over 500w PEP driven the same. The PA500WH broadband HF amp did about 330Wpep but it does need more drive above 20m. I was testing all these amps on 11m.
Bottom line on this Amp is that it runs too hot at 400w. Not sure what the design output is ..I guess 75 X 4 would make it 300W…I think I was driving her a tad hard with 30w input…started to smell smoke! It really needs a fan on top and bigger/better heat sinking. Devices are too close to each other….thermally speaking! Perhaps a large piece of copper to disperse the heat. No problem at all on Sideband.